The present invention relates generally to a method for detecting a road grade or pitch angle being experienced by a moving vehicle. More particularly, the present invention relates to a method for detecting the road grade angle under dynamic lateral operating conditions for use in a motor vehicle having a vehicle dynamics control system.
Automotive vehicles with braking systems which respond to vehicle conditions as well as driver input have been produced. For example, when a particular yaw rate is desired, as indicated by a driver""s steering wheel operation, if the vehicle is not producing an adequate yaw rate, the braking system or steering system of the vehicle may compensate by altering a particular wheel speed or steering angle, respectively. This control is dependent on accurate measurement of several vehicle operating conditions.
One important condition is the pitch of the vehicle which corresponds to the pitch of the road. The pitch angle of the vehicle is the angle or corresponding front to rear change in elevation of the vehicle. Because this parameter may not easily be directly measured, it can be improved by inferring or calculating from other signals available in the vehicles. Because the vehicle is operated under a wide variety of conditions, calculations made from the various sensors may vary in accuracy. For example, steady straight or steady state turning may result in varied accuracy. The pitch determination may be used in various safety systems within the vehicle.
It would be desirable to provide a method for determining a pitch angle experienced by a motor vehicle that is robust to dynamic lateral vehicle operating conditions under a wide variety of maneuvers while providing an indication as to the accuracy at the given time.
There is disclosed herein a method for detecting a pitch angle experienced by a motor vehicle. The method comprises the steps of:
generating a longitudinal velocity signal corresponding to a longitudinal velocity of the vehicle;
generating a derivative signal corresponding to a derivative of said longitudinal velocity;
generating a yaw rate signal corresponding to vehicle yaw rate;
generating a lateral velocity signal corresponding to the lateral velocity of the vehicle; and
determining a vehicle pitch angle based in response to said derivative signal, said yaw rate signal and said lateral velocity signal.
In a further aspect of the invention, a control system for an automotive vehicle includes a longitudinal accelerometer that generates a longitudinal acceleration signal corresponding to a longitudinal acceleration of a center of gravity (COG) of the vehicle body. A lateral velocity sensor/observer generates a lateral velocity signal corresponding to the lateral velocity of the vehicle body. A controller is coupled to the yaw rate sensor, the longitudinal accelerometer and the lateral velocity sensor. The controller determines a longitudinal speed from the longitudinal acceleration signal. The controller determines a vehicle pitch angle in response to the longitudinal speed, the yaw rate signal and the lateral velocity signal.
One advantage of the invention is that a pitch angle may be derived from the various sensors while also providing an indication of pitch angle error. Another advantage of the invention is that calibration of the system sensors may also be performed using the teachings of the present invention.
Other aspects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.